It has been known for many years that placing a lubricant, such as oil or grease, between the surfaces of two adjacent materials will cause the coefficient of friction between the two materials to be reduced. Thus, the force required to drag or push one material across or past another is clearly minimized. The properties of the lubricant such as viscosity, density and the like, can be varied as desired. Furthermore, it has been known for many years that friction between two materials can be reduced by using anti-friction (ball or roller) bearings between them.
The coefficient of friction between two materials can vary depending upon the properties of the materials and their outer contacting surface finish or rugosity. For instance, the coefficient of friction between construction grade steel plates or pipes is about 0.3 to 0.5 if they are dry or with just water lubrication. With oil or grease and/or certain plastic coatings on the contacting surfaces, the coefficient of friction has been found to be as low as 0.15.
It has also been known to use plastic beads, such as divinyl benzene styrene (Teflon added) materials in essentially spherical form to reduce friction between materials. For example, thermoplastic material of this type having bead diameters of 0.010 to 0.025 inch has been mixed with oil field drilling mud and used to lubricate and reduce the friction between the mud itself and the sides of a drilling pipe in which the mud is used in connection with a drilling operation. These styrene beads are held in random suspension in the mud and thus do not form a "pure bearing." Similarly, these styrene beads have been used for water surfactant in water treatment plants, but again, the styrene beads do not operate in a "pure bearing" manner. Styrene beads of this type have been made and sold under the trademark Lubra-Glide by Sun Chemical Products Corp, New Orleans, La. 70130.
Steel balls in grease have also been experimentally used with heavy loads in slow oscillatory motion. This concept has been described in an article appearing in a periodical entitled "Mechanical Engineering," December 1974, pages 27-30.
Some power companies have experienced failures of unprotected high voltage (300-525 Kv) armored cables in submarine crossings due to scour, ships dragging anchors and the like. To give these cables more protection, efforts have been expended in forcing such cables through conduits or pipes laid over the crossing route. This has been limited to relatively short distances due to the weight of the cable, the friction between the cable and the conduit, and the resultant tension required to move the cable through the conduit. Some cable must be spliced at spaced locations along its length due to length limitations of presently available cables. The outer surface coating of the cable must be sufficiently abrasive-resistant to prevent damage to the cable as it is being pulled or pushed through the conduit. An obvious limitation on conventional pipe-enclosed cables has been the length of any continuous stretch of such a cable being restricted to about one mile due to the high friction load of pulling the cable through the conduit. Also, the increase in friction at bends in the conduit require additional effort to force the cable through the conduit.
Attempts have been made in the past to "float" a cable or a gutline-enclosed cable through a conduit, such as a pipeline. U.S. Pat. No. 4,048,807 discloses this concept using a dense slurry or drilling mud to create a substantially neutral buoyancy to essentially suspend the cable within the conduit. However, the maximum reach of such an installation has been calculated to be about four to five miles due to the high coefficient of friction between the cable and the conduit using slurry or drilling mud.
Because of the foregoing limitations in the prior art, a need has existed for an improved product and for a method for use in decreasing the coefficient of friction between an inner member, such as a smaller pipe or an electrical cable of the type described, as it is pulled or otherwise moved along a support or through a larger conduit, such as an underground or an undersea pipeline.